Graphene oxide decorated with fullerenol nanoparticles for highly efficient removal of Pb(II) ions and ultrasensitive detection by total-reflection X-ray fluorescence spectrometry

In this paper, the graphene oxide (GO) decorated with fullerenol nanoparticles C60(OH)22 has been designed for the highly selective separation and ultrasensitive determination of lead ions. The grafting fullerenol nanoparticles to the surface of GO solves the problem of their high solubility in aqueous solutions and simultaneously uses their high hydrophilicity and deprotonation ability. The research has revealed unique adsorption properties of GO-C60(OH)22 toward Pb(II) ions at pH 5.5, i.e., minimal adsorbent dose (5 mg L−1), impressive resistance to ionic strength (up to 1 mol L−1), and enormous adsorption capacity (1307 mg g−1), much higher than those of any of the currently reported sorbents. The adsorption isotherms, kinetics, and effect of ionic strength indicate that an inner-sphere model based on surface complexation is the main mechanism of Pb(II) adsorption on GO-C60(OH)22. The high-resolution O1s and Pb4f X-ray photoelectron spectra confirm the strong chelation of Pb(II) ions and suggest the various coordination of Pb(II) ions to the oxygen functional groups. The exceptional properties of GO-C60(OH)22, including the possibility of application in micro-quantities, were the basis for the development of the method for ultra-sensitive detection of Pb(II) ions using such micro-analytical technique as total-reflection X-ray fluorescence spectrometry (TXRF). The method allows obtaining an extremely low detection limit of 2.3 pg mL−1 using a low-power TXRF instrument. Due to the impressive selectivity of the method, the ultra-trace Pb(II) ions can be highly accurately determined in complex matrix samples, including high salinity waters challenging to analyze using other analytical techniques.